I've been searching the forums and online, without luck, for ideas on how to finish and treat a cement ceiling. My HT project is in a room under the garage and the prefabricated slabs can't be nailed into or modified in any way really, except gluing to -- and I'm not sure what will stick and hold for very long.

I'm really interested in what some of the acoustic guys would recommend I look at doing. The ceiling is almost smooth so it wouldn't take much to finish it if smoothing something on it is a good idea. I do worry that something too thin would be too reflective as the room current has a 5 second flutter with nothing but one person in it. I'm not sure if some acoustic panels are the right choice, or just in first reflective, or if the ceiling should have little treatment because ceilings are normally reflective in dedicated HT's.

http://i261.photobucket.com/albums/ii57/distoga/IMG_0587.jpg

I'm currently planning on treating behind the false wall and the other three walls up to ear level with 1" fiber and have bass traps behind the false wall in the corners, floor to ceiling.

Thanks.

More photos and pictures of my theater design are in my sig if they're needed to help me figure out what to do with the ceiling.

What are the current space dimensions. If you have the height you can give up a few inches and put your joists on top of your walls so you end up with a true "room in a room" design.

First let me ask you this, how would you like to finish the ceiling, drop ceiling, sheetrock etc...? There are several ways to make things work for you but the above question will help us to help you.

The room is 15'10" wide, 21'7" long and the height is 8'3" on top of the footers and 8'3" at the back of the room (the ceiling slopes down towards the front so water drains out of the garage).

I considered framing the walls and running boards between the sides but decided against it because of the weight of sheet rock would require to be 2x6's or 2x8's and I already lost 2' of ceiling height because of a builder error.

The idea I like most is putting curtains around the room (to cover the concrete walls) and "apply" something to the ceiling to minimize losing any more height than I already have. Some ideas I've found could be to stucco the ceiling (depending on if a stucco crew can get it to stick), but I'm not sure if stucco would be a good acoustic choice. I've wondered about acoustic tiles but that could make a huge dent in my budget. I've wondered if there is some type of plaster that would be spread and smoothed to make the ceiling look flat and have an acoustic benefit.

There is a spray on acoustical insulation intended for concrete ceilings. You see it most often in commercial spaces. Worth some calls. I think you can even get it in black.

One product:

http://www.internationalcellulose.com/home/products/k-13/

As I mentioned in another thread....

People out here in the US southwest... Adobe and stucco that stuff all the time. I actually think many of these I have seen personally had awesome accoustics.

IIRC forum member Zinema did his room with concrete walls and ceiling. His thread is really detailed.

Zinema Construction thread (http://www.avsforum.com/avs-vb/showthread.php?t=726456)

You can stick pretty much anything to cement with Liquid Nails. :D

--Ethan

Wow, 3 hours to get through Zinema's thread, but it was worth it. It looks like he did particle board suspended about 2/3rds an inch off the ceiling.

Is there much difference between mdf, particle board, how thick they are and the spacing? He said he chose it to limit low bass but wouldn't that thickness stop mids and highs?

If I have curtains around my theater do I need extra bass trapping to equal things out?

What about 1" acoustic fiber up to ear level behind the curtains?

I'm guessing the no one would disagree with the two side bass traps behind the false wall but again is 1" acoustic fiber on the entire front wall too much for mids and highs?